-LRB- CNN -RRB- -- A New Zealand teenager has been questioned in connection with a scheme by hackers to remotely take over more than 1 million computers worldwide and use them for criminal activity , New Zealand police and the FBI said Thursday .

FBI Director Robert Mueller says botnets are `` the weapon of choice for cyber criminals . ''

The FBI has identified at least 2.5 million unsuspecting computer users who have been victims of so-called `` botnet '' activity . Hackers install viruses , worms and other attack programs that allow them to take over the computers and use them to commit cyber crimes .

Industry numbers suggest there are as many as 5 million infected computers .

The FBI tracked down the teen and believes the 18-year-old , known by the cyber alias `` AKILL , '' was the ringleader of an international botnet group know as the `` A-team , '' responsible for infecting more than 1 million computers .

Authorities seized computer equipment and questioned the teen , said New Zealand Police Detective Inspector Peter Devoy , but the person has not been identified , arrested or charged . Watch how botnet attacks occur ''

Internet addresses and information furnished by the FBI led to the teenager , Devoy told CNN .

`` Today , botnets are the weapon of choice for cyber criminals , '' said FBI Director Robert Mueller in a statement . `` They seek to conceal their criminal activities by using third-party computers as vehicles for their crimes . ''

Personal computers can be compromised when users open an attachment , click on an advertisement or give personal information to a `` phishing '' site , or a fake site that looks legitimate . The FBI advises users to protect themselves by updating their anti-virus software , installing a firewall , using non-common passwords and avoiding suspicious e-mail attachments and advertisers ' links .

In 2005 the FBI launched Operation Bot Roast to combat botnet attacks , which the bureau estimates have caused $ 20 million in losses and theft , including one scheme that bilked a Midwest financial institution out of millions . Since June , eight people have been charged or convicted of crimes related to botnet activity .

Between January and June , Symantec Corp. , a leading computer security company , detected more than 5 million bot-infested personal computers carrying out at least one attack a day , according to the company 's September report .

That was a 17 percent decrease form the previous reporting period , according to Symantec , which said hackers appeared to be abandoning the technique because of strengthened security and law enforcement initiatives .

China had the most infected computers at 29 percent , followed by the United States at 13 percent , Symantec reported . However , 43 percent of the servers used by hackers to operate the hijacked computers were located in the United States , Symantec said . E-mail to a friend

CNN 's Kevin Bohn contributed to this report .

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NEW : Internet addresses and information furnished by the FBI led to the teen

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FBI believes New Zealand teen was the ringleader of the `` A-team ''

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Botnet attacks cause $ 20 million in losses and theft , the FBI estimates

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Symantec detected more than 5 million bot-infested personal computers this year